A polyalkylene oxide is water-soluble and thermoplastic, therefore, the polyalkylene oxide is used for uses such as a viscous agent for papermaking, a ceramic binder, a polymerization stability assistant and a material for a pharmaceutical preparation. When the polyalkylene oxide is used as a thickener such as a viscous agent for papermaking and the like, generally, the polyalkylene oxide having a high molecular weight is preferable from the viewpoint of a viscosity control. As a production method of the polyalkylene oxide having a high molecular weight, a method using a catalyst obtained by the reaction of an organozinc compound with an aliphatic polyhydric alcohol and a monohydric alcohol has been reported (refer to patent literature 1).